FIELD OF THE INVENTION AND DESCRIPTION OF RELATED ART
The present invention relates to high temperature heat resistant acrylic polymers preferably made through free radical polymerization of methyl methacrylate (MMA) and related acrylates with maleimide (MI) and related maleimides through an extremely high conversion bulk polymerization process to produce extremely pure, improved acrylic copolymers.
The acrylic copolymers of the present invention have approximately the same physical properties as conventional acrylic polymers except that the present invention polymers have high purity, a higher glass transition temperature, better impact resistance, higher heat distortion temperatures, and in the case of preferred polymers, excellent clarity.
In general, acrylics are well known and have excellent optical properties and weatherability for numerous uses such as in lighting fixtures, automobile tail light lenses, dials, video discs, opthalmic contact lenses and numerous other articles where durable, weatherable, clear features are desired.
In order to obtain specific optimized physical properties for acrylics, it has been known to polymerize different monomers to form copolymers. The art of copolymerization had an early start in polymer technology when it was found that copolymerization of a mixture of two or more monomers led to polymers which had different and/or more suitable physical properties than either of the homopolymers alone or a mechanical blend of polymers formed from the individual monomers.
Poly (methyl methacrylate) (PMMA) is the most popular commercial polymer in the acrylic industry at present. The relatively high clarity and excellent light transmission of PMMA, i.e., transparency, coupled with its resistance to sunlight and low density make this polymer ideally suited to production of automobile tail light lenses, dial covers, lighting fixtures and other related articles. PMMA has excellent weather resistance, durability and is pleasing in appearance when formulated into relatively thick sections and these features render PMMA and related acrylics ideal for such end uses.
In the context of the present invention, the term transparent refers to the property of the copolymers of the present invention to be transparent to light and specifically refers to the fact that the preferred copolymers of the present invention have transparency properties about the same as the transparency properties of conventional PMMA.
The heat distortion temperature (HDT) of PMMA copolymers is satisfactory for most uses for relatively short times at temperatures of 90.degree.-102.degree. C. (195.degree.-295.degree. F.). The glass transition temperature (Tg) of PMMA copolymers is generally between 85.degree.-105.degree. C. However, for relatively long time periods and/or for lighting systems in which relatively great amounts of heat are produced by the lamps, such as, for example, in mercury vapor lighting systems, the glass transition temperature and heat distortion temperature of conventional PMMA copolymers are unsatisfactorily low.